This invention relates to a product feeding device included in a combination weigher for feeding product adequately to each of a plurality of weighing units thereof. More specifically, this invention relates to a product feeding device provided with a revolving product detector for detecting the amount of product to be fed to each weighing unit to control adequately the same.
As shown in U.S. Pat. No. 4,664,200, for example, a combination weigher having a plurality of circularly arranged weigh units includes a plurality of radially arranged vibratory conveyer troughs for feeding product to the respective weigh units and a central vibratory dispersion feeder for distributing product to the conveyor troughs, The central dispersion feeder disperses product uniformly to all conveyor troughs. However, only selected conveyor troughs are driven during each combination operation, namely, those troughs corresponding to the weigh units which are unloaded during that cycle of operation. Since the weigh units are usually not selected uniformly during a succession of cycles of operation, uneven and excessive amounts of product tend to accumulate in the conveyor troughs. This can result in excessive amounts of product being loaded into the weigh units. Such nonuniform feed to the weigh units is liable to happen also when the product is massive or lump-shaped and, in a serious case, the maximum feed may be as much as five times the minimum feed. Such variance of feed is undesirable since it reduces the weighing accuracy and lowers the working efficiency of the weigh units.
In the device of the above-cited reference, the thickness of the product layer on the dispersion feeder is detected by an optical detector to control the amount of feed to the dispersion feeder and, on the other hand, the exit of the dispersion feeder to each conveyer trough is provided with a shutter which is opened and closed in synchronism with operation of the corresponding conveyer trough, thereby preventing undesirable feed from the dispersion feeder to the conveyer troughs. Even in this case, however, excessive amounts of product can accumulate inside the shutter and fall off at once on the conveyer trough when the shutter is opened, thereby resulting in nonuniform feed to the corresponding weigh happer.